Identification of bacteria not readily identified by current commercially available identification kits often is a time-consuming and difficult task. In most laboratory settings, these organisms need an experienced and expert microbiologist or technologist for reliable and accurate identification. We have attempted to make these identifications more readily and accurately available using less well-trained technologists by adapting computer-assisted identification methods for these purposes. Identification of four major groups of bacteria is now possible using specifically-developed computer programs. These are Gram positive rods (90 different species); fastidious Gram negative rods (46 different species); nonfermentative Gram negative rods (64 different species) and enteric Gram negative rods (81 different species). Each program was developed using the minimum number of tests and enough of an array to tests to permit adequate discrimination between the organisms in each data base. Tests were also selected on the basis of their ease of performance and ready availability to routine diagnostic laboratories. All 4 programs are currently being used and seem to yield useful identification results. The suggested identifications are used by the technologists as guidelines for further tests if necessary, although the identifications are usually definitive enough so that further testing is unnecessary.